The present invention constitutes an improvement on the polycentric hinge disclosed in U.S. Pat. No. 5,443,444, issued Aug. 22, 1995.
As described in said patent, the human knee joint provides for relative articulation of the upper and lower legs, between the femur and tibia, through a plurality of centers or axes over an arc of about 180°. To effectively duplicate the movement of the human knee joint when necessary to mechanically assist the knee, for example, following injury or a surgical procedure, the art has developed articulated knee supporting braces embodying plural axis or polycentric hinges worn about the knee of the patient. These hinges may be used to support the knee joint throughout its full range of motion, or to lock the knee joint in a selected position, or to limit the allowed range of motion of the joint to less than complete extension (straightening) and/or to less than complete flexion (bending) of the knee. During rehabilitation, it is common to initially limit articulation of the knee and to progressively increase the permitted range of motion in gradual increments as healing progresses.
Examples of prior art developments in knee braces may be found in U.S. Pat. Nos. 5,292,303 to Bastyr, et al., U.S. Pat. No. 401,933 to DeCamp, U.S. Pat. No. 5,062,858 to Broeck et al., U.S. Pat. No. 4,732,143 to Kausek et al., U.S. Pat. No. 5,038,763 to Wiggins, U.S. Pat. No. 4,726,361 to Farley, U.S. Pat. No. 4,628,916 to Lerman et al., U.S. Pat. No. 3,817,244 to Taylor, U.S. Pat. No. 3,901,223 to May, U.S. Pat. No. 4,372,298 to Lerman, U.S. Pat. No. 4,493,316 to Reed et al., and British Patent No. 1,316,572 and French Patent No. 1,187,444, among others. Some of these patents disclose knee braces with polycentric hinges and others have hinges with a single axis of rotation.
U.S. Pat. No. 5,443,444 discloses a polycentric hinge for orthopedic knee braces comprising two rigid support arms having cooperating, interlocking, continuously abutting proximal ends rotateably connected to one another by a polycentric hinge assembly including a pair of pivot pins and a hinge plate. Each rigid support arm is rotatably coupled at its proximal end to the hinge plate by a respective one of the pivot pins. The two arms are pivotable about their respective pivot pins along equal arcs of movement between an adjustable extension position and an adjustable flexion position. The total range of motion of the hinge is from substantially complete extension to substantially complete flexion; the rigid arms being positioned in substantially straight line end-to-end relationship in the complete extension position and being positioned in substantially side-by-side relation in the complete flexion position. The hinge accommodates relative angular movement of the rigid support arms substantially between 0° and 180°. The hinge plate is provided with a plurality of adjustment apertures arranged in an angularly spaced apart pattern for reception of a pair of limit pins to intercept rotation along the arc of rotation of at least one of the arms, thereby to limit rotation of both of the arms.
The proximal end portion of the one arm includes an extension facing edge and a flexion facing edge; the extension facing edge being adapted to engage a limit pin in the direction of extension movement and the flexion facing edge being adapted to engage a second limit pin in the direction of flexion movement. The pins, extending through the apertures into which they are inserted, thus restrain movement of the arm beyond the positions defined by the respective limit pins.
Adjustment of the permitted range of motion is obtained by repositioning the pins from one aperture to another to adjust the arc of rotation of the pair of arms, preferably in 15° and/or 30° increments, between a final extension position and a final flexion position. Each of the apertures may be labeled according to a specific angular position for extension or flexion, promoting convenient adjustment.
An openable cover member, specifically a flip-top cap, is provided to allow selected access to the limit pins for purposes of adjustment and to normally overlie the pins and prevent inadvertent or accidental displacement of the pins from their intended positions of adjustment. Also, each of the limit pins is attached to a respective pivot pin by an individual electrometric tether to retain the limit pins against loss or misplacement, while at the same time allowing the limit pins to be appropriately positioned among the apertures.
The flip top cap or cover for the limit pins, unfortunately, is not particularly secure and is prone to popping open, particularly during contact sports, thereby openly exposing the limit pins and permitting the pins to be inadvertently disassociated from their respective apertures, whereupon the hinge is incapable of achieving its intended purpose (unless intended for complete flexion and complete extension). The hinge, until reset, fails its purpose, during which time the knee intended to be protected could suffer further trauma.